Field of Invention
The present invention relates to a power converting circuit and a control method thereof. More particularly, the present invention relates to a resonant DC/DC power converting circuit and a method for controlling the same.
Description of Related Art
With the progress of science and technology, energy conversion and employment have become increasingly important. Among the various energy conversion technologies, since the resonant converters can achieve zero voltage switching (ZVS) and zero current switching (ZCS), devices are allowed to operate at a low turn-off current and high frequency. Therefore, resonant converters have been widely applied to high efficiency and high power density power supplies.
However, when a single phase resonant converter is applied to a low voltage high current output, the current stress of the output capacitor is higher, which requires more capacitors connected in parallel to satisfy the requirements. As a result, a defect is generated. In order to overcome such a defect, N resonant converters identical to one another may be connected in an interleaved parallel manner. As such, the N phase resonant converters connected in parallel are able to reduce the overall current ripples and voltage ripples as compared with the single phase converter so as to reduce electromagnetic interferences. As a result, volumes of passive devices including inductors and capacitors are decreased to increase the dynamic response speed. In addition to that, the N phase resonant converters connected in parallel can operate alternately at the same time to improve the efficiencies of the converters and the power density.
In practical applications, parameters of the interleaved parallel converter circuit unavoidably have deviations. Hence, how to use an active current-balance control to balance the output powers of the converters has become a major issue confronted by the industry. Generally speaking, a traditional pulse width modulation (PWM) converter can realize current balance of the parallel module through adjusting the duty ratio owing to its fixed switching frequency. Although a resonant converter controls its output power through controlling the switching frequency, it is required that driving signal frequencies of switches of the converters are equal and have a phase difference of 180°/N to achieve the best current ripple cancellation effect of the converters connected in parallel when implementing the resonant converter. As a result, the switching frequency of the converters needs to be adjusted simultaneously, which causes that the resonant converter cannot achieve current balance through adjusting the duty ratio like the PWM converter and needs to adjust signal frequencies to achieve the objective of current balance.
For the forgoing reasons, there is a need to resolve the above-mentioned inconveniences and shortcomings by providing a resonant DC/DC power converting circuit and a method for controlling the same, which is also an objective that the relevant industry is eager to achieve.